Daniel of Brantham near Ipswich denied kerb-crawling or any sexual activity and claimed he only wanted her to take him to a burger van early on June 10.

But he was found guilty by Ipswich magistrates last September and fined £325 with £450 costs and a £15 victim surcharge.

Married father-of-two Daniel had his appeal dismissed at Ipswich Crown Court and was ordered to pay another £400 costs in November.

A Metropolitan Police disciplinary tribunal has now allowed him to say in the force, but has demoted him to be a detective constable.

A Met spokesman said: "Mr Daniel has been reduced in rank from a detective sergeant to a detective constable and his suspension has been lifted." Daniel had been placed on restrictive duties after his arrest.

The decision to allow him to keep his job was slammed by an Ipswich prostitute who now sits on a steering group trying to help vice girls in the town give up the sex trade.

Charlotte said: "A former vice squad officer knows it's against the rules. I thought he'd be kicked out of the force for that because it's blatant disrespect for the rules.

"All people will see from this that a police officer can get caught for kerb-crawling and still keep his job.

"He's had a slap on the wrist and told not to do it again. It doesn't send a good message. It just says, 'Don't worry about it'."

Daniel, who now faces a pay cut, refused to comment yesterday at his home.

Ipswich Borough Council leader Liz Harsant said: "Maybe he's learnt from his mistakes. I'm not quite sure taking his job away from him would have been the right answer.

"It's a disgrace in itself to go down a rank in the police force and he will have to live with that."

Ipswich Labour MP Chris Mole said: "What he did was very stupid and not really the sort of conduct you expect of a police officer, particularly one who's worked in that area.

"I think it's a fairly serious punishment. I don't know what extenuating circumstances he may have put before the tribunal."

Daniel is among 120 people arrested by Suffolk police for kerb-crawling related offences since the launch of a crackdown following the murders.

Ipswich magistrates heard how Daniel was followed by police as he drove Miss Drewry to an industrial estate where he paid her £20.

Mrs Drewry claimed she masturbated him and was attempting oral sex on the front seat of the silver Skoda estate when the two police cars screeched up.